How to recognize Limp Mode at the track and what to do about it.

[Dave B]

I tried posting this on the problems section of this forum but didn't get much response.

Thought guys concerned about suspensions are more likely to be tracking their cars and running in to limp mode

So I know the car has issues with cooling at the track and it is possible that a vented hood and a PWR radiator may help but what I want to know is, what happens when the car goes in to limp mode.

1) does it suddenly lose power? If so, how much? i.e. does it make you unsafe until you can cool down?
2) do you get a dash light and if so what does it look like? Any warning before it triggers?
3) how long to get out of limp mode? Do you have to stop and let the engine cool or will it revert to normal within a lap or so?
4) what are the triggers? ( I know this is a tough one because there are likely a number of triggers and a true measure of oil temps is not one of them)

I am concerned that if the car suddenly loses power that the guy following me particularly in a high speed corner will be totally surprised if all of a sudden I appear to unintentionally slow down.

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[fatherpain]

Hello Dave,
I am by no means an expert on the matter, but have had (4) track days and encountered limp mode once, at my 2nd event.

My understanding is limp mode can be triggered by:

1. overheating - @Lust recently proved this can be solved by adding:

• PWR or C&R Racing Race Radiator
• Oil cooler
• Vented hood
• Open grill

opening the hood between sessions helps. Running heater on high helps. Acuity Reverse hoses may also help a little. If you are tracking and notice the heat climbing on the temperature gauge, ease up a little and do a cool down lap.

2. Fuel starvation. Our fuel gauge is Not designed for the huge lateral G’s during track driving... so can give erroneous readings. Can be remedied by adding a fuel surge tank, but that’s pretty hard core...For regular folks just be sure to gas up between sessions

When I hit limp mode, it was instantaneous and I received a scary CEL regarding the turbo. From that point, the car acted like it had a Governor device and my revs were limited. The maximum speed I could sustain was 70 mph until reaching the pits. No fun when other cars can get up to 130 at certain spots on the track. Fortunately it occurred late in the day and there weren’t many cars driving with me. The CEL popped up after about 15-17 continuous laps.

When I pulled off, my fuel gauge read 3/4 full. The tank level nosedived to 1/4 while driving to the gas station about 2 miles
away. After filling up and clearing the code, the CEL never returned.

Before going hog wild on mods, suggest trying it at the track first to see how it is...Preferably in the spring when it’s cooler. Depending on your pace, these issues may or may not pop up.

Then again if want to be sure, the cooling solution is listed above

 

[kefi]

solid pooooost @fatherpain

 

[Lust]

Two ways to trigger limp mode

1. Reaching excessively high ECT / overheat
2. Fuel starve by not topping off fuel between sessions.

Both will result in a ton of errors on the dash. They can easily be reset by disconnecting the battery for a few minutes. They will not go away on their own.
There’s a rev limiter and speed limiter. You’re literally limping the car back to a safe place. Can’t exceed 4000-4500 RPM IIRC.

If you have good awareness you can tell when your car is going to hit limp mode. Top off fuel between each session especially if you’re an experienced driver. High G corners are what causes the fuel starve on pretty much anything below half tank for me.

I would recommend keeping the temp gauge below 3/4 at all times. Better if you have a way to readout the actual coolant temperature itself and try to keep it below 230 ish.

 

[kefi]

Two ways to trigger limp mode

1. Reaching excessively high ECT / overheat
2. Fuel starve by not topping off fuel between sessions.

Both will result in a ton of errors on the dash. They can easily be reset by disconnecting the battery for a few minutes. They will not go away on their own.
There’s a rev limiter and speed limiter. You’re literally limping the car back to a safe place. Can’t exceed 4000-4500 RPM IIRC.

If you have good awareness you can tell when your car is going to hit limp mode. Top off fuel between each session especially if you’re an experienced driver. High G corners are what causes the fuel starve on pretty much anything below half tank for me.

I would recommend keeping the temp gauge below 3/4 at all times. Better if you have a way to readout the actual coolant temperature itself and try to keep it below 230 ish.

I've been looking for solid info like this myself for the longest.. been missing this info in the tuning megathread. I don't track yet, myself.

Thanks so much dudes.

 

[Dave B]

Being the cheapskate that I am, was wondering if just the radiator or just the vented hood alone would work. I am not so sure that adding an oil cooler would work if it is coolant temp that triggers limp mode. After all the car has to get rid of heat one way on another and it seems that air flow exit from the engine bay after the radiator is a significant factor in causing issues. For my time attack series a bigger radiator is no issue but a vented lighter hood increases the car's class even though it likely helps with aero as well as engine overheating.

 

[Lust]

Radiator is top priority
Next would be vented hood, specifically Varis because of where the vent is located
Finally oil cooler helps because oil temps get hot on track and it will also help reduce ECT. This is because the radiator is also cooling down oil. If the oil is being cooled with its own heat exchanger, the radiator needs to do less work.

 

[NapalmEnema]

Everything I've read - oil cooler seems to be the most important part - then additional venting / radiator.

 

[Dave B]

Everything I've read - oil cooler seems to be the most important part - then additional venting / radiator.

If the oil cooler is mounted remotely out of the engine bay and is getting different air, then sure but if it is in the engine bay, can't see why it would do a better job than a bigger radiator. Also most oil coolers are pretty small compared to radiators so not sure if the added heat exchange capacity would be all that great. If the issue is air not getting out of the engine bay and backing up pressure, then a vented hood will improve the efficiency of all coolers as well as prevent some front end lift.

 

[NapalmEnema]

If the oil cooler is mounted remotely out of the engine bay and is getting different air, then sure but if it is in the engine bay, can't see why it would do a better job than a bigger radiator. Also most oil coolers are pretty small compared to radiators so not sure if the added heat exchange capacity would be all that great. If the issue is air not getting out of the engine bay and backing up pressure, then a vented hood will improve the efficiency of all coolers as well as prevent some front end lift.

The ones I see that are interesting to me are mounted behind the front fake light, so def out of the engine bay area. I'm sure there are a lot of solutions that 'aren't' lol - but the one I was looking at was def out of the bay.

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